Exit polls are not final, and official results will be released in coming hours.

Putin has dominated Russian politics for 18 years and was already the country’s longest-serving leader since Soviet dictator Joseph Stalin.

Putin’s critics have slammed the election as unfair, citing the Kremlin’s tight control over the media, quelling of the opposition and restrictions on some election monitors to ensure a free vote.

Opposition activists and the non-governmental election monitoring group Golos reported voting irregularities. By early evening Sunday, Golos had counted 2,000 incidents, including observers being prevented from carrying out monitoring.

The vote was a huge logistical undertaking, taking place across Russia’s 11 time zones over 22 hours, in around 97,000 polling stations, according to the Central Election Commission.

There was little fanfare in the campaign period and Russian news was dominated by developments in political crises between Russia and Western powers.